H1 antihistamines (first-generation)
- H1 blockers that readily enter the CNS
- Sedation + antimuscarinic effects are common
- Diphenhydramine/hydroxyzine are prototypes
- Useful for itch, motion sickness + short-term sleep
- Falls/delirium risk rises in older adults
- Often poor chronic-allergy choices
Class at a glance
- H1 blockers that readily enter the CNS
Practical pearls
- Diphenhydramine/hydroxyzine are prototypes
Clinical role
- Useful for itch, motion sickness + short-term sleep
- Often poor chronic-allergy choices
Safety / monitoring
- Sedation + antimuscarinic effects are common
- Falls/delirium risk rises in older adults
Self-check
- What commonly limits first-generation H1 antihistamines?
Sedation and antimuscarinic effects. - Which patients have greater falls/delirium risk from these drugs?
Older adults.
Drugs in this class (9)
H1 antihistamines (first-generation) prescription history
Animated chart of estimated U.S. prescriptions per year, H1 antihistamines (1944–2026). Older H1 highlighted from 1944.
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